1. Field of the Invention
The present invention relates to a method and an equipment for preparing photo- or thermally-imagable, negative working patterning compositions.
2. Brief Description of Art
Thermally sensitive, negative working printing plates are generally made with patterning compositions that are imaged on a substrate. These patterning compositions commonly contain light-sensitive material that is a mixture of an acid generator, a cross-linking resin or compound, a binder resin and an infrared (IR) absorber. The thermal sensitivity of the resulting printing plate enables them to function, but for some new applications, may be detrimental to their performance, processability and shelf life. For instance, in digital laser imaging applications, the window of operation of these commonly used patterning compositions was found to be dependent on the amount of heat these compositions were exposed to during the imaging process. When inadequate levels of heat were applied to the imaged areas during IR or UV/visible radiation imaging, then incomplete image formation or weak images may result on the printing press. If the non-imaged areas of patterned compositions were exposed to either extreme temperatures for short periods or to prolonged times of moderate heat during standard processing, storage or shipping of the printing plates, then these non-imaged areas may be difficult to be removed with standard developing techniques. The use of digital laser imaging technology, which employs higher power (and greater thermal energy) than previous used imaging equipment, has accentuated these undesirably effects and therefore decreased this window of operation.
The Kodak Polychrome Graphics Computer to Plate All-In-One (CTP1) printing plate machine available from Kodak Polychrome Graphics of Norwalk, Conn. was designed to provide the printing plate market with a single piece of equipment possessing all necessary components for the processing of printing plates utilizing a patterning composition in an expedient manner while at the same time having small footprint. The CTP1 has successfully accomplished this desired result, but its window of operation is not as wide as desired. The CTP1 printing plate machine is described in U.S. patent application Ser. No. 09/573,126, filed on May 17, 2000.
Other references that further show the state of the thermal plate and other printing plate arts include the following:
U.S. Pat. No. 4,020,762 (Peterson) teaches making an imaged planographic printing plate that employs a patterning layer containing a diazo sensitizer, carbon particles and a self-oxidating binder (e.g. nitrocellulose). Portions of the patterning layer are ablatively imaged by means of laser beam, followed by flood exposing the plate (and imaged patterning layer) with UV light and then developing the plate to cause the imaged areas struck by the laser to accept ink and the non-image areas to accept water. This U.S. patent does not incorporate a preheating step in its process.
U.S. Pat. No. 4,356,254 (Takahashi et al.) is directed to an image-forming method wherein a light-sensitive material comprising a support having a light-sensitive layer provided on the support. The light-sensitive layer containing a quinonediazide sensitizer. This light-sensitive material is imagewise exposed with a high intensity energy beam (e.g. a laser beam) to make the o-quinonediazide compound alkaline soluble in those areas that are imaged; then overall heating the light-sensitive material to insolubilize the exposed areas; then overall exposing (flood exposing) the thus-processed material with light to solubilize unexposed areas; and then developing with an alkaline developer to provide a negative image by removing alkaline soluble areas of said layer. This reference does not teach employing acid generator-type light sensitive layers.
U.S. Pat. No. 4,356,254 (Stahlhofen et al.) describes a process for producing negative relief copies using a light-sensitive material that contains either a benzoquinone diazide compound or a naphthoquinone diazide compound. This process includes the steps of imagewise exposing the light-sensitive material; then heating the light-sensitive material; then flood exposing the thus processed material which is followed by developing the material, whereby the layer areas which were not struck by light in the first imagewise exposure are washed off. This reference uses quinone diazides as the sensitizers in the light-sensitive material and does not teach the use of acid generator-type sensitizer.
U.S. Pat. No. 4,927,741 (Garth et al.) describes a method for the reversal of photosoluble lithographic printing plates having an aromatic quinone diazide-containing coating. This method includes the steps of (1) imagewise exposing a portion of the coated surface with UV lamp to render that portion soluble in a developer; (2) heating the plate and coating to render the imagewise exposed relatively insoluble in the developer; (3) then overall irradiating the coated surface to solubilize the remaining portion of the coated surface not previously exposed, wherein the overall irradiation step (3) is applied through water. This process does not teach the use of acid generator-type sensitizers, but instead is limited to quinone diazide sensitizers.
U.S. Pat. No. 5,380,622 (Roser) describes the production of negative relief copies of a recording plate that uses naphthoquinone diazide compounds as the photosensitive compounds. This process includes the step of: (1) imagewise exposing the recording plate using UV, metal halide, xenon or arc lamps; (2) then heating the exposed plate; (3) then uniform exposing the plate to the same light source used in the imagewise exposure; and (4) then developing the thus-processed recording plate with an aqueous alkaline developer to dissolve the alkali-soluble components and form a negative relief copy. This process also does not teach the use of acid generator-type sensitizers, but is limited to quinone diazide sensitizers.
U.S. Pat. No. 5,631,119 (Shinozaki) teaches an image formation process that employs photosensitive composition layer containing a quinone diazide photosensitizer and includes the steps of: (1) exposing the entire surface (flood exposing) of the photosensitive composition layer, to light rays (normally at 290 to 500 manometers) that render the quinone diazide compound soluble in an alkaline developer; (2) then imagewise heating the flood exposed photosensitive composition layer (such as with a thermal head printer); and (3) then developing with an aqueous alkaline solution.
Japanese Published Patent Application No. 11190902 A2 (Kunio) teaches making a heat mode recording lithographic printing plate having a image forming layer containing a quinone diazide compound and an infrared absorber. This plate is formed by (1) imagewise exposing the image forming layer with laser beams; (2) then flood exposing it to ultraviolet rays; and (3) then developing it with an aqueous alkaline developer.
Japanese Published Patent Application No. 267266 A2 (Mitsumasa) teaches a method for making lithographic printing plates that includes the steps: (1) imagewise exposing a photosensitive layer to visible laser beams; (2) then developing the imagewise exposed photosensitive layer; and (3) then flood exposing the developed photosensitive layer to UV light.
Japanese Published Patent Application No. 089478 A2 (Yasuo) teaches a method for making a photopolymerizable printing plate wherein a photosensitive layer is imagewise exposed to specified exposure light using a laser, then developed and then flood exposed to light at least 100 times the quantity employed in the imagewise exposure.
Accordingly, there is a need for a processing improvement that will widen the window of operation of these standard patterning compositions particularly in equipment such as the Kodak Polychrome Graphics CTP1 printing plate machine, thereby increasing their shelf life, processability, chemical resistance and the performance of printing plates that employ such patterning compositions. The present invention provides an excellent solution to that need.
Therefore, one aspect of the present invention is directed to a method for imaging patterning compositions comprising the steps of:
(1) providing at least one patterning composition layer on a hydrophilic substrate which can be used as a lithographic base; said patterning composition comprising:
(a) at least one thermally activated acid generator;
(b) at least one cross linking resin;
(c) at least one binder resin comprising a polymer containing reactive pendant group selected from group consisting of hydroxyl, carboxylic acid, sulfonamide, active imide, alkoxymethylamide and mixtures thereof; and
(d) at least one infrared absorber;
(2) imagewise exposing the patterning composition layer to actinic radiation;
(3) treating the imaged patterning composition layer with heat energy to treat the imaged portions of the composition layer;
(4) flood exposing the heat-treated, imaged patterning composition layer with UV light for a predetermined time, said time being sufficient to promote the effective clear-out of non-imaged portions during the following developing step (5) without causing substantial deterioration of the imaged portions; and
(5) developing the flood exposed, heat-treated, imaged patterning composition with an aqueous alkaline developer to remove the non-imaged areas of the patterning composition layer and leaving the imaged areas substantially unaffected.
A second aspect of the present invention is directed to an assembly for imaging patterning compositions comprising:
(A) a hydrophilic substrate which can be used as a lithographic base and having at least one patterning composition layer thereon, said patterning composition comprising:
(i) at least one thermally activated acid generator;
(ii) at least one crosslinking resin;
(iii) at least one binder resin comprising a polymer containing reactive pendant group selected from the group consisting of hydroxyl, carboxylic acid, sulfonamide, active imide, alkoxymethylamide and mixtures thereof,
(iv) at least one infrared absorber;
(B) source of actinic radiation;
(C) means for imagewise-exposing the patterning composition layer with actinic radiation;
(D) means for heat-treating the imaged patterning composition layer;
(E) source of UV radiation;
(F) means for flood exposing the heat-treated, imaged patterning composition layer with the UV radiation;
(G) means for developing the flood exposed, heat-treated, imaged patterning composition layer to remove the non-imaged areas of the patterning composition and having the imaged areas substantially unaffected.
The method of the present invention widens the window of operation of standard used patterning compositions used in making thermally sensitive printing plates. In particular, this method will improve the Kodak Polychrome Graphics CTP1 processing system. The CTP1 system is a single piece of equipment that possesses all necessary components for making printing plates using standard patterning compositions. This method of the present invention will significantly open the window of the operation of the CTP1 processing system without changing it through-put or its footprint.